The present invention relates to wireless local area network apparatus.
A wireless local area network commonly comprises a plurality of communication stations located in a Basic Service Area (BSA). The stations can send and receive communication signals via a base station and, in this manner, the base station receives the signals from a station in the BSA and re-transmits the signals to the intended recipient station.
The BSA can be provided as one of a plurality of BSAs which together form an Extended Service Area. In this case, the base station of each BSA may comprise an access point for a backbone infrastructure for connecting the BSAs for allowing communication between stations in different BSAs within the Extended Service Area.
Communication between stations, whether by way of a base station or otherwise, can require synchronization between a transmitter of one station or an access point and a receiver of another station. Disadvantageously, accurate synchronization between a transmitter and a receiver in a BSA cannot be readily achieved due, in particular, to operational limitations such as transmission and reception delays and delays in accessing the wireless medium.
It is an object of the present invention to provide wireless local area network apparatus having improved synchronization between the transmitters and the receivers in the network.
According to the present invention there is provided wireless local area network apparatus comprising transmitter means and receiver means, characterized in that said transmitter means includes transmitter timer means for controlling periodic generation of transmission signals, said receiver means includes receiver timer means, and said transmitter means has means for including transmitter timer data in said signals for synchronizing said receiver timer means with said transmitter timer means, said transmitter timer data representing the state of said transmitter timer means at the time of transmission of the signal in which it is included.
The wireless local area network apparatus of the present invention is particularly advantageous for power management applications in which low power portable wireless stations are employed in the BSA. The stations periodically switch between a low power consumption state, in which their transceivers are de-energized, and a high power consumption state, in which their transceivers are energized, and can thereby receive periodic signals transmitted from some other station. The synchronization between the signals transmitted from some other station and the switching of the power-consumption state of the receiver stations is advantageously achieved by the apparatus of the present invention. The improved synchronization of the present invention allows for operation of the stations in a wireless local area network with reduced power-consumption, which is particularly important for stations having an on-board power supply.
The apparatus of the present invention can be advantageously employed to control other timing relationships between a transmitter and a receiver in a wireless local area network. For example, in so-called frequency-hopping devices, the transmission frequency employed by a transmitter is periodically changed and so a receiver has to adapt to this change in communication-signal frequency. The apparatus of the present invention allows for accurate synchronization between the operational changes in the transmitter and receiver during such frequency hopping.